Aircraft engine components, and similarly the components of many other high performance machines, are manufactured so as to avoid sharp edges and tight corners, as sharp edges and tight corners are areas where stress concentrations can occur increasing the possibility of crack formation. Part edges are often chamfered or radiused to dull sharp edges thereby reducing the probability of crack formation. Accurate measurement of edge and corner radii is important to ensure component quality.
Presently used methods for measuring the radius of edges and corners include the use of hand held pre-cut radius gauges and the use of wax impressions. Radius inspection with pre-cut radius gauges involves placing different gauges of known radii in contact with the part surface and back illuminating the part and gauge. The part edge is assumed to have the same radius as a gauge which, when placed in contact with the part edge, allows no light to pass through the region where the gauge contacts the part surface. This method of measuring edge or corner radii is not practical or accurate when measuring small radii or compound radii.
Simple and compound radii can be measured by forming a wax impression of the part surface. The wax impression must then be evaluated on an optical comparator, usually located in an area removed from the part location. The accuracy of such radius measurement depends upon the judgment and interpretation of the operator of the optical comparator. The process is often slow, subjective, labor intensive and eye fatiguing.
In some situations coordinate measuring machines can be utilized to measure part radius. Coordinate measuring machines produce adequate results but are expensive, have a slow processing rate and are not easily adapted to the production environment.
The complex geometries of aircraft engine components adds complexity to the measurement of edge and corner radii by any of the procedures discussed above. Part surfaces may contain compound curvatures and edges and corners which are difficult to access. The parts themselves are often difficult to handle and manipulate.
The present invention provides a fast and accurate means for measuring edge and corner radii, solving many of the problems associated with previous inspection methods.